TCB: A Puzzling Puzzle
Comments(5) 
I reached the end of The City Beneath over the weekend — it’s definitely a much easier game than Journey to Rooted Hold. But before talking about that, I’d like to describe a room in the final descent that left me baffled, even after solving it: Abyssian Fortress, 2S.
The basis of this room is that there are these nine 4×4 cells of tarstuff, three of each of the three varieties (tar, mud, and gel). The only monsters in the room are the Mothers in each cell, visible as a pair of eyes, that make the tarstuff expand every 30 turns, although the way they’re penned in here keeps them from expanding. Access out of the room is controlled by force arrows and a black gate, which only opens when all the tarstuff in the room has been cleared. And most of the floor is missing, so you have to get around by means of a 4×4 raft. So far, so straightforward. This much makes it a solid but not-too-difficult tar-clearing puzzle. The only tricky part is the gel. Gel is only vulnerable at its interior corners, but the cells here don’t have any. To get started, you have to create some by letting the gel expand onto your raft, which immobilizes the raft until it’s cleared. But even that’s just low-level tactics.
The difficulties come in with some things you have to step on to get started. First of all, there’s a disarm token, which takes away your sword. Stepping on a disarm token again restores your sword, but the force arrows around the token here prevent you from doing that. Then there’s a mimic potion, which lets you place a mimic on any clear spot on the floor. Mimics imitate your movements, and are armed with swords, so you can use that to clear the tar even when disarmed. But the circumstances suggested another possibility: what happens when a mimic steps on a disarm token? I knew that there exist things that mimics trigger just as if you had stepped on them. So I tried this, and sure enough, I got my sword back. Unfortunately, that left me in a difficult position for the next obstacle: the bridge.
Bridges are another new concept in TCB. They act kind of like level 2 of Donkey Kong: you can remove the supports by walking on them. (In fact, the game reuses the familiar trap door tiles to represent the supports.) Once the supports are all gone, the whole thing collapses, killing anything on it, including Beethro if you’re foolish enough to step back onto the bridge from the last support. In this room, there’s a bridge that’s blocking the raft from moving, and the trap door to collapse it is on the opposite end of the bridge from the raft. Getting a mimic from the disarm token all the way to the other side of the bridge without going there yourself seems impossible — the only way to enlarge the distance between yourself and a mimic is to move in a way the mimic can’t, typically by pulling it against a wall, and there are no suitably-positioned walls in that part of the room. Doing it the opposite way, collapsing the bridge personally and leaving the mimic on the raft, is feasible, but leaves you stranded on a little 2×2 platform, without enough movement room to make the mimic navigate the raft over to you. No, the easier approach, I decided, was to create the mimic on the 2×2 platform where it could free the raft, and remain swordless while it fought the tar for me.
At first, I tried just standing on the raft with the mimic while it fought the tar, but it proved difficult to protect my defenseless body this way. Eventually I got a bright idea: There’s another raft over on the right side. If I got that free, the mimic could take one raft into the fighting zones while I stand on the other, a comfortable distance away. This worked, and I cleared the level through, in effect, remote telepresence. But there were still things about the puzzle that I didn’t understand. For starters, there’s a red gate over on the right side, enclosing the platform corresponding to the one I didn’t want to get stuck on in the previous paragraph. Why is that there? It controls access to an empty space. I cleared the room without opening it. It could be a mere red herring, but DROD doesn’t usually go in for that. Or when it does, it does it with things that give you the wrong idea about a puzzle and cause you to attempt it the wrong way, not with confusing elements that don’t suggest a solution at all.
And then, after you solve the room, there’s a Challenge scroll. The challenge: Clear the room without moving the mimic over the disarm token. In other words, the thing that I had decided was impossible is apparently the normal solution. I feel like I still haven’t solved this room, despite having solved it the hard way. And I have no idea which way I solved it the first time through.
Would this work?
Go across disarm tile and potion.
Go to upper right corner of nearby raft.
Create mimic on disarm tile, reclaiming sword.
Go down three, so you and the mimic are on either side of the force arrow.
Go left and up; mimic can’t go up, because of the wall.
Go left and right. Mimic can’t go right, because of the force arrow. Mimic should be one square below you.
Cross the bridge with you on the top row and mimic on the bottom row.
Go down one square so you’re on the pink trapdoor tile and the mimic is one tile below, one square above the trapdoor.
Walk back across the bridge (on the bottom row). Mimic can’t go right, because of the pit, so it stays one square above the trapdoor.
When you get back to the raft, move down. The mimic steps on the trapdoor, collapsing the bridge and freeing the raft with you (and your sword!) on it.
Even if that works, it doesn’t explain the red gate, though….
Your last paragraph reminds me of an experience I just had with Stephen’s Sausage Roll. I’ve been replaying it, and I was stuck for several days on Ancient Dam, which has a fairly straightforward mechanism for getting from one side of the level to the other. (Fairly straightforward as things in the last sequence of Stephen’s Sausage Roll goes.) But I could not get it to work right this time, so I tried lots of other things, and eventually hit on a method that didn’t use like half the ladders in the level and which took a lot of fiddling. After this I went online to look at solutions, and found three, none of which was the one I’d just done. I’m pretty sure the first time I did the one marked “intended solution,” which used the mechanism I mentioned in about the way you’d expect it to be used.
…the problem is that the bridge is only one tile wide, right? What I thought was the top row is scenery.
The main reason that won’t work is that it heavily relies on the idea that the bridge has a top row and a bottom row, but in fact it has only one row. Only the planked part, level with the second row of the raft, is the bridge. The row above that is part of the underpinnings of the wall to the north, as you can see by comparing it to the other walls.
As for the motivation behind the design, I’ve just found this on the Caravel forum:
I haven’t seen the “Watcher’s demo” referred to here, but at least the intent behind the red gate is explained: you were supposed to need to open it to get back on your raft after dropping the eastern bridge. But in fact you can just step from the raft to the trap door and right back onto the raft.
That description seems to imply that the Challenge here was the intended solution, though.
Yes, I noticed that flaw after posting. My ability to figure out puzzles in a game I haven’t played yet seems to be limited. (Also, some time I should stop fighting the inevitable and start playing these.) Oh, and I just realized that I’m completely confused about how trapdoors work, which I really should know from the Web DROD that I’ve played.
I did find a post which refers to “Not using the second platform or rearming yourself,” which does sound like a more challenging challenge is that basically the “protect your defenseless self on the platform” issue? I can’t completely make sense of that forum post; presumably before they added the mimic there wasn’t a disarm token? And then you were supposed to both have swords, but it was too hard to coordinate them both fighting the gel? But once you add the second platform, isn’t it basically back to the same situation as the original gel puzzle that was too hard, except for telepresence?
Don’t underestimate the power of telepresence. Remotely controlling a mimic has one big advantage over being there yourself: monsters do not attack mimics. Thus, they can cut up gel in situations where there’s not enough room to flee from the monsters it creates.
Also, by now I’ve watched a demo of how to rearm yourself and get the raft free. The steps are:
1. Spawn the mimic and get it to walk over the disarm token
2. Get the mimic immediately to the right of you
3. Cross the bridge with the mimic and get onto the island (moving diagonally so you don’t step on the trap door)
4. By means of some fiddly maneuvering, get the mimic one space below you
5. Cross back over the bridge, leaving the mimic behind
6. Make the mimic step on the trap door, collapsing the bridge